News Release Number: STScI-2005-28

Spitzer and Hubble Team Up to Find "Big Baby" Galaxies in the Newborn Universe

September 27, 2005: Astronomers have used the penetrating power of two of NASA's Great
Observatories, the Spitzer and Hubble Space Telescopes, to identify one
of the farthest and most massive galaxies that once inhabited the early
universe. Conventional wisdom is that galaxies should have grown up more
slowly, like streams merging to form rivers. But this galaxy appears to
have grown very quickly, within the first few hundred million years
after the Big Bang. By contrast, our Milky Way galaxy took billions of
years to grow to its current size, through devouring smaller galaxies.
The galaxy was pinpointed among approximately 10,000 others in the
Hubble Ultra Deep Field (UDF), presently the farthest optical and
infrared portrait of the universe ever taken.

Q & A: Understanding the Discovery

1.
How do astronomers know the galaxy is so far?

When a galaxy is very distant, it appears very red. This is because of
two effects: (i) The expansion of the universe streches the light to
longer (redder) wavelengths, and (ii) Intervening hydrogen gas absorbs all
the ultraviolet light that the galaxy emits. In this particular case,
only infrared light is reaching us, indicating that the galaxy is either
very distant or extraordinarily obscured by dust.

2.
How do astronomers know the galaxy is so massive?

The mass of a galaxy, in terms of its number of stars, can be estimated
from the amount of light it radiates. The more stars of a certain temperature,
the brighter the galaxy.

3.
Why did the universe make galaxies so soon after the Big Bang?

As the universe expanded and cooled from the primeval fireball, hydrogen
atoms formed when hydrogen atomic nuclei captured free floating electrons.
This neutral hydrogen then collected along great filaments of dark matter,
an unknown form of invisble matter that first coalseced after the Big Bang.
The gravitationally collapsing hydrogen triggered a firestorm of star birth.
The stars formed small clusters that then coalesced to make larger galaxies.